Which of the following is NOT a main symptom of carbon monoxide poisoning?

Carbon monoxide (CO) poisoning is characterized by a range of symptoms that result from the body's inability to transport oxygen effectively due to the binding of CO to hemoglobin in red blood cells. Among the common symptoms are headache, nausea, and tightness across the forehead, which are direct responses to reduced oxygen delivery to the brain and other tissues.

A headache is a frequent symptom because the brain is particularly sensitive to changes in oxygen levels. Nausea can occur as a result of the body's overall stress response to low oxygen levels, and tightness across the forehead may be experienced as a form of tension or pressure due to cerebral hypoxia.

The presence of a skin rash, however, is not associated with carbon monoxide poisoning. A rash typically points towards allergic reactions, infections, or other dermatological conditions rather than the physiological effects of CO exposure. Therefore, identifying a skin rash as a symptom of carbon monoxide poisoning is incorrect, as it does not align with the established medical understanding of how CO affects the body.